1. Field of the Invention:
The present invention relates to a syringe pump for sucking and discharging a fluid, which is used for an automatic analyzing apparatus.
2. Description of the Related Art:
Conventionally, there is a syringe pump for sucking and discharging a fluid, which comprises a lead screw connected to a rotational shaft of a motor, a moving element screwed to the lead screw, a piston mounted to the moving element and a cylinder in which the piston slides. Generally, since the lead screw in a driving side and the piston in a load side have parallel axes to each other, the load from the piston uniformly acts on the driving side so that there is problems in a quantitative accuracy and a durability, for example, engagement between the lead screw and the moving element lacks smoothness, rotation of the motor lacks in uniformity and the like.
Then, as disclosed in U.S. Pat. No. 4,475,666, an apparatus in which the axes of the driving side and the load side are linearly disposed on a line so as to coincide the axis of the drive side with the axis of the load side has been considered. The apparatus comprises a sleeve 29 having a threaded portion in an inner peripheral portion, a nut 25 engaged with an inside of the sleeve 29, a piston 16 provided in a center of the nut 25 and movable within an inner portion of a cylinder 15 and a motor 33 for rotating the sleeve 29 through a belt 32 meshed with an outer peripheral lower portion of the sleeve 29, in which the motor 33 is disposed side by side with the sleeve 29. Further, two brackets 34 extends through the inside of the sleeve 29 from an upper portion of the sleeve 29 and are fastened to each other in a lower portion of the sleeve 29 by a plate 36 so that when the sleeve 29 is rotated, the brackets 34 restrict the rotation of the nut 25 and act as a rotation preventing means for introducing the nut 25 in an axial direction of the sleeve 29. The outer peripheral lower portion of the sleeve 29 is supported by a radial ball bearing 30.
In the above syringe pump, since the motor 33 and the sleeve 29 are disposed side by side in a lateral direction although the axis of the piston 16 and the axis of the sleeve 29 are disposed on a line, the apparatus is totally widened toward the lateral direction, thereby preventing a miniaturization. Accordingly, it can be considered that the motor 33 is disposed immediately below the sleeve 29 so as to directly rotate the sleeve 29, however, since the bracket 34 extends through the sleeve 29 in a vertical direction, it is difficult to rotatably hold the sleeve 29.
On the contrast, since the sleeve 29 is pivotally supported in the lower portion of the body thereof, the sleeve 29 is easily swung in a radial direction and an axial direction, particularly, the upper portion thereof is swung in a radial direction so that a straight drivability of the piston 16 is hardly secured, thereby generating problems in view of the quantitative accuracy and the durability.